1. Field of the Invention
The present invention relates to a sulfonium compound having two acid sites that produce two different photo-acid generators in one molecule, a photo-acid generator containing the sulfonium compound, and a method for producing the photo-acid generator. More particularly, the present invention relates to a sulfonium compound which can address the problem of using a mixture of two different photo-acid generators, has excellent compatibility with the resist, and can produce an excellent resist pattern when applied as a photo-acid generator, and to a photo-acid generator containing the sulfonium compound, and a method for producing the sulfonium compound.
2. Description of Related Art
Semiconductor microprocessing technologies utilize lithographic processes, and in such lithographic processes, chemically amplified resist compositions are extensively used. Such a chemically amplified resist composition contains a photo-acid generator, which is a compound capable of generating an acid when irradiated with light.
When such a photo-acid generator absorbs light that is irradiated in a semiconductor patterning process, the photo-acid generator generates an acid.
In the case of an onium salt, which is one of photo-acid generators, the onium salt is degraded into a cation form or a radical form as a result of light irradiation, and exits in a different molecular form, and an acid is generated at the anion side, so that diffusion of acid occurs on the resist film at the time of wafer baking after light irradiation.
The photo-acid generator exerts direct influence on the resist pattern characteristics such as the resolution and line edge roughness (LER) of resists, due to various characteristic factors such as the ability to absorb light, the acid generation efficiency, the diffusion capability of the generated acid, and the strength of the anionic acid.
A conventional photo-acid generator has a molecular structure which is capable of generating only one type of acid. Thus, in order to obtain a high degree of resolution, when acid generators having all of the characteristics such as high diffusibility, low diffusibility, high permeability and low permeability are needed, the process of mixing acid generators and using a mixture thereof has been complicated and troublesome. Furthermore, in the case of using a mixture of acid generators, the acid generators may not be uniformly mixed in the resist, thereby rather causing a problem that a resist pattern having uniform characteristics cannot be obtained.
As an example of existing photo-acid generators, Korean Patent Application No. 10-2006-00133676 discloses a compound represented by the following formula:
wherein X represents an alkylene group or a substituted alkylene group; Y represents a hydrocarbon group having 5 to 30 carbon atoms and containing one or more aromatic rings; Q1 and Q2 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms; A+ represents an organic counterion; and n represents 0 or 1.
In another example, Korean Patent Application No. 10-2007-0062926 filed by Shin-Etsu Chemical Co., Ltd. discloses a compound represented by the following formula:R1COOCH2CH2CF2CF2SO3−M+  [Chemical Formula]wherein R1 represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 15 carbon atoms, or a heteroaryl group having 4 to 15 carbon atoms; and M+ represents a lithium ion, a sodium ion, a potassium ion, an ammonium ion, or a tetramethylammonium ion.
It is described in the patent application filed by Shin-Etsu Chemical Co., Ltd. that the sulfonic acid represented by the above formula can exhibit strong acidity and can have a variety of substituents introduced thereinto, and that the degree of freedom in the design of molecule is high.
However, the conventional constitutions of photo-acid generators have problems that, in order to obtain high resolution, a photo-acid generator having a high diffusion rate and a photo-acid generator having a low diffusion rate, and a photo-acid generator having high permeability and a photo-acid generator having low permeability need to be used in mixture. Thus, when two or more kinds of photo-acid generators are used as a mixture in order to obtain a photo-acid generator having contradictory characteristics as described above, there is a problem that it is difficult to obtain uniform compatibility in the resist.